Proposed work is designed to study neuroanatomical structures and circuitory involved in somatic water activity in primates. The red nucleus of the midbrain has been the focus of initial studies. Its efferent connections are under investigation using autoradiographic techniques after stereotactic injections of tritiated amino acids into both the rostral and caudal parts of the red nucleus in the rhesus monkey. In this species, the two major output neuronal types of the red nucleus are separated such that cells with fine Nissl material occupy the rostral part and cells with coarse Nissl material occupy the caudal part. Thus the connections of these populations can be investigated independently. The cytoarchitecture of the red nucleus also is being examined in the chimpanzee and human. Its efferent connections will be studied in material prepared by the Fink-Heimer method for anterograde degeneration in a single chimpanzee with a stereotactic lesion produced in the rostral part. Research is commencing on the efferent projections of the pedunculopontine nucleus in the monkey. This structure is the site of termination of descending fibers from both the red and subthalamic nuclei.